This invention relates generally to development systems using donor rolls for ionographic or electrophotographic imaging and printing apparatuses and machines, and more particularly is directed to a method to improve the appearance of a ghosting print defect in such a developer unit.
Generally, the process of electrophotographic printing includes charging a photoconductive member to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive surface is exposed to a light image from either a scanning laser beam, an LED source, or an original document being reproduced. This records an electrostatic latent image on the photoconductive surface. After the electrostatic latent image is recorded on the photoconductive surface, the latent image is developed. Two-component and single-component developer materials are commonly used for development. A typical two-component developer comprises magnetic carrier granules having toner particles adhering triboelectrically thereto. A single-component developer material typically comprises toner particles. Toner particles are attracted to the latent image, forming a toner powder image on the photoconductive surface. The toner powder image is subsequently transferred to a copy sheet. Finally, the toner powder image is heated to permanently fuse it to the copy sheet in image configuration.
One common type of development system uses one or more donor rolls to convey toner to the latent image on the photoconductive member. A donor roll is loaded with toner either from a two-component mixture of toner and carrier or from a single-component supply of toner. The toner is charged either from its triboelectric interaction with carrier beads or from suitable charging devices such as frictional or biased blades or from other charging devices. As the donor roll rotates it carries toner from the loading zone to the latent image on the photoconductive member. There, suitable electric fields can be applied with a combination of dc and ac biases to the donor roll to cause the toner to develop to the latent image. Additional electrodes, such as those used in the Hybrid Scavengeless Development (HSD) technology may also be employed to excite the toner into a cloud from which it can be harvested more easily by the latent image.
A problem with donor roll developer systems is a defect known as ghosting or reload, which appears as a lightened ghost image of a previously developed image in a halftone or solid on a print. The defect is due to the different characteristics of the toner that has been reloaded onto the recently detoned areas of the donor roll.